1. Field of the Invention
The invention relates to the field of imaging, an in particular to apparatus for large area imaging.
2. Description of the Art
Imaging systems are used in a wide range of applications, particularly for imaging for medical diagnosis, in biotechnology, and in industrial applications for non-destructive testing and on-line product quality control. For all of these fields of application, the prevailing means of performing imaging has been to use radiation, usually X-rays, gamma-rays and beta-rays. Radiation is detected by some sort of imaging plane, which need not be planar. Accordingly, the term imaging surface will be used hereinafter. Images are formed either directly on the imaging surfaces (e.g., projection imaging) or data are processed and images are reconstructed in a computer (e.g., computerized tomography or coded aperture imaging in nuclear medicine).
Traditionally, the imaging surface was formed by a film in a cassette. Other imaging surface solutions have been developed over the past 40 years offering digital imaging. Such examples are NaI scintillating screens, NaI scintillating crystals, BGO crystals, wire gas chambers, digital imaging plates etc. More recently, semiconductor imaging solutions such as Charged Coupled Devices (CCDs), Si microstrip detectors and semiconductor pixel detectors have been developed.
Typically, in all of the above cases, when a large imaging area is needed it is made either as a monolithic structure (e.g., films, digital imaging plates, NaI screens, etc.) or as a mosaic of smaller pieces (tiles) put together and fixed on a support surface (e.g., gamma cameras with NaI crystals). When a monolithic large imaging surface is employed, if a part of the surface is defective then the whole surface needs to be changed. Unfortunately, the most precise digital on-line imaging devices proposed so far involve pixel-based semiconductors which cannot be manufactured in large areas (larger than a few square cm at most). Moreover, it would not be desirable to manufacture, for example, a monolithic 30 cm by 30 cm digital imaging semiconductor surface because the yield would be low. If a portion of the expensive imaging area became defective, then the whole surface would have to be replaced.
It has been proposed to provide a large area imaging surface (larger than a few square mm) using a tiling approach. The applicants own patent application WO 95/33332 proposes such an approach. Using such an approach, individual imaging devices are arranged in an array, or mosaic, on an imaging support to form a large area imaging mosaic. Outputs from the individual imaging devices can be processed to provide a single output image corresponding substantially to the whole area covered by the imaging surface. However, when the imaging devices are tiled to form such a mosaic, dead spaces are left around the active imaging areas of the imaging devices. In order to deal with this problem it is proposed to stagger adjacent rows of imaging devices in the array and to provide for relative movement between an object to be imaged and the imaging array. Although such an approach does give good results and means that the effect of the dead spaces can be at least substantially eliminated, this does require the provision of a mechanism for the relative movement and appropriate software for processing the resultant multiexposure image.
There is thus a need for an improved imaging system and method which, while providing the advantages of the tiling approach, remove or at least mitigate the problems of previous tiling approaches.
According to embodiments of the present invention, an imaging apparatus includes an imaging support and a plurality of imaging device tiles. Each tile includes an imaging device having an imaging surface and has a non-active region at or adjacent an edge of the file. The imaging device on the tile mounted on the support may be tilted, or angled, such that part of the imaging surface of one tile at least partially overlies the non-active region of another tile, thereby providing substantially continuous imaging in a first direction. Such embodiments provide a new imaging mosaic system for producing imaging mosaics using a plurality of imaging devices tiles and an imaging support in a manner which reduces or substantially eliminates the dead spaces between tiles.
According to one particular embodiment, which enables the use of a planar support, each tile includes a mount having a mounting surface for mounting the tile on the support and a device support structure for carrying the imaging device on the mount such that the imaging surface is tilted with respect to the mounting surface. The support structure may be an intermediate member between the imaging device and the mount, and may be wedge-shaped to fully support the imaging device. However, alternatives are possible, for example spacers at one end of the tile.
In an alternate embodiment directed to the use of planar tiles, each tile includes a mount having a mounting surface for mounting the tile on the support. The support provides a plurality of respective tile mounting locations on a support surface, the mounting locations being tilted to provide sawtooth deviations from the support surface. The imaging surface of each imaging device may thus be tilted with respect to the support surface.
The mount in such embodiments may be planar, and may be implemented using, for example, a printed circuit board. The imaging devices may also be planar, and may include, for example, a planar detector layer overlying a planar image readout layer, a surface of the detector layer forming the imaging surface. The detector layer can provide a plurality of detector cells and the readout layer can provide a plurality of corresponding readout circuits, each readout circuit being coupled to a respective detector cell. In a particular embodiment, the detector layer is substantially rectangular, the readout layer is substantially rectangular and has a connection region which extends beyond the detector layer at one end thereof, the mount is substantially rectangular and has a connection region which extends beyond the readout layer at the one end, wired connections are provided between the connection regions of the readout layer and the mount, and the non-active region of the tile comprises the connection regions of the readout layer and the mount. The tile may be elongated in the first direction (i.e., the direction of substantially continuous imaging) to minimize the angle of tilt and any effects of parallax. Moreover, the tiles may be mounted on the support such that the detector layers of adjacent tiles extend in a second direction perpendicular to the first direction so as to almost or actually touch each other.
The imaging devices may be positioned and held on the support in a reversible and non-destructive manner. For example, an arrangement for mounting the imaging devices may allow individual imaging devices to be removed multiple times so that the same imaging device can be used in a different imaging support or it can be replaced if found to be defective without damaging the imaging support and without affecting the operation of any other imaging device on the imaging support. The support may provide a plurality of tile mounting locations, with the mounting arrangement removably mounting a respective tile at each location.
According to another particular embodiment, each tile mounting location may include a plurality of support contacts, each for co-operating with a respective tile contact for a transfer of signals between the support and the tile. The support contacts may be recesses for receiving correspondingly shaped bumps on a tile, or bumps for receiving correspondingly shaped recesses on a tile. The support contacts may also be resilient conductive members overlying contact pads.
In yet another embodiment, the imaging apparatus may include a separate insulating substrate, which is located between the imaging device tile(s) and the imaging support and is aligned to enable electrical contact between each support contact and a corresponding tile contact via a respective resilient contact member. In this embodiment, each resilient conductive member is a ring having a hole for aligning bumps of the tile contacts or of the support contacts with corresponding contacts of the support, or corresponding contacts of the tile, respectively. The resilient conductive members may be conductive rubber, conductive polymers or metal springs.
The mounting arrangement may be adapted to apply an adjustable mounting force for removable mounting a tile at a tile mounting location. The mounting arrangement may include a hole for each file mounting location, the hole being of appropriate diameter to accommodate securing member protruding from the tile. A fastener for engaging with the securing member can be provided for each hole on the support at each tile mounting location. In a particular embodiment, the fastener is a nut and the securing member is a screw, the nut being adapted to be tightened on the screw after the imaging device tile has been positioned on the tile mounting location with the screw extending through the hole, whereby the nut is used to secure the tile at the tile mounting location with an adjustable mounting force. Alternatively, the mounting arrangement may include a screw located or locatable at each imaging device tile location, for engaging with a threaded hole in a mount of an imaging device tile.
According to another embodiment, the imaging apparatus may include a plurality of different imaging supports and a common set of imaging device tiles which are mountable on a selected imaging support at any one time, but are removable, whereby they may be mounted on another one of the imaging supports. An imaging support for apparatus such as those described above may provide a plurality of respective tile mounting locations on a support surface, the mounting locations being tilted to provide sawtooth deviations from the support surface. The support may include an arrangement for mounting an imaging device tile at each mounting location in a non-destructive, removable manner. The support enables the use of a planar imaging device tile.
An imaging device tile for imaging apparatus such as those described above may include an imaging device having an imaging surface, a non-active region at or adjacent an edge of the tile, a mount having a mounting surface for mounting the tile on an imaging support and a structure for supporting the imaging device on the mount such that the imaging surface is at an angle to the mounting surface. This form of imaging device tile enables the use of a support which does not have sawtooth deviations for the tile mounting locations.